Seismic valves are valves which automatically close and shut off flow of natural gas or other media during and after an earthquake. If pipes or fittings are cracked or broken by an earthquake, a seismic valve can shut off flow and prevent leakage to reduce the threat of explosion and fire. Seismic valves typically have pendulums, balls or other inertial elements which undergo relative movement with respect to other valve components, during an earthquake, to close the valve.
A disadvantage of many seismic valves is that the entire valve unit has to be level for the valve to properly operate. Consequently, the pipe (e.g., a natural gas pipe) on which the seismic valve is installed must be vertical plumb. In addition, certain seismic valves may inadvertently reopen if the valve body is rotated much beyond 45.degree. from vertical, which rotation may occur when a building foundation collapses in an earthquake.
Certain seismic valves also have a large cover requiring a large seal area. In a fire, large seals can result in large gas leaks, an inherent potential safety problem. The large cover is also disadvantageously under media (e.g., gas) pressure when the valve is closed.
In various seismic valves, friction in pivot joints can cause tripping or closing of the valve at unintended seismic acceleration levels, i.e., the valve closes under unduly low levels of seismic shock and vibration, or it fails to close when it should at higher seismic movements. In addition, friction in pivoting or rotating joints in ball or plug type seismic valves may prevent complete closure of the valve. Certain prior art valves also incur relatively large pressure flow losses of gases or liquids through the valves, due to the valve configuration.